Hitherto, coil components such as an inductor, a transformer, and a choke coil, have been used in various articles such as household electric appliances, industrial equipment, and vehicles. A coil component includes a magnetic core and a coil fitted to the magnetic core. As this magnetic core, a ferrite magnetic core, which is excellent in magnetic property, shape flexibility and costs, has widely been used.
In recent years, a decrease in the size of power source devices of electronic instruments and others has been advancing, so that intense desires have been increased for coil components which are small in size and height, and are usable against a large current. As a result, the adoption of powder magnetic cores, in each of which a metallic magnetic powder is used, and which are higher in saturation magnetic flux density than the ferrite magnetic core, has been advancing. As metallic magnetic powders, for example, pure Fe particles, and Fe-based magnetic alloy particles such as those of Fe—Si-based, Fe—Al—Si-based and Fe—Cr—Si-based alloys are used.
The saturation magnetic flux density of any Fe-based soft magnetic alloy is, for example, 1 T or more. A magnetic core using this alloy has excellent DC superimposition characteristics even when made small in size. In the meantime, the magnetic core is small in specific resistance and large in eddy current loss since the core contains a large quantity of Fe. Thus, it has been considered that unless grains of the alloy are coated with an insulator such as resin or glass, it is difficult to use the magnetic core for any article for which a higher frequency than 100 kHz is required. However, a magnetic core in which Fe-based soft magnetic alloy grains are bonded to each other through such an insulator may be poorer in strength than ferrite magnetic cores by an effect of the insulator.
Patent Document 1 discloses a magnetic core obtained by using a soft magnetic alloy having a composition of Cr: 2 to 8 wt %, Si: 1.5 to 7 wt % and Fe: 88 to 96.5 wt %, or Al: 2 to 8 wt %, Si: 1.5 to 12 wt % and Fe: 80 to 96.5 wt %, and heat-treating a compact made of grains of the soft magnetic alloy in an atmosphere containing oxygen. When the temperature of the heat treatment is raised to 1000° C., the breaking stress of the resultant magnetic core is improved to 20 kgf/mm2 (196 MPa). However, the specific resistance thereof is remarkably lowered to 2×102 Ω·cm, so that the magnetic core does not sufficiently endure both of the specific resistance and the strength.
Patent Document 2 discloses a magnetic core obtained by: applying a heat treatment at 800° C. or higher in an oxidizing atmosphere to an Fe—Cr—Al based magnetic powder including Cr: 1.0 to 30.0% by mass and Al: 1.0 to 8.0% by mass and including the balance of the core consisting substantially of Fe, thereby self-producing an aluminum-including oxidized coat film on the surface of the powder; and further solidifying and compacting the magnetic powder by discharge-plasma sintering in a vacuum chamber. This Fe—Cr—Al based magnetic powder may contain one or two of Ti: 1.0% or less by mass, and Zr: 1.0% or less by mass, and may contain, as an impurity, Si: 0.5% or less by mass. However, the resistance value of this magnetic core has as low as several milliohms; thus, the magnetic core is unsatisfactory for being used for any article for which a high frequency is required, or for the case of forming electrodes directly onto the surface of the magnetic core.